Baltimore County police believe that a 64-year-old Randallstown woman attacked near her home Thursday night is the fourth victim of an assailant who already has raped one woman and sexually assaulted another in the area since early September.

According to police, the woman who was attacked Thursday night had gone shopping in Pikesville and returned home about 11:15 p.m. After she unlocked her door, her assailant sneaked into her house and then attacked her as she returned with some groceries, police said. The attacker fled when the woman pushed a security alarm.

Sgt. Stephen R. Doarnberger, a police spokesman, said the assailant, usually armed with a knife, targets women returning home from shopping. In each of the four instances the attacker waited to make sure no one else was at home before making his move, said Sergeant Doarnberger. Two of those attacked managed to ward off the attacker by telephoning for help or by sounding a private security alarm.

In light of the attacks, police urge women to take precautions, such as shopping with a friend or having someone meet them when they return home. "It looks like he waits to see if they have anyone helping them," the sergeant said. "Then, if they have to use a key [to open the door] he figures they are alone."

Police said the man, described as a black male, about 30 years old, 6 feet 3 inches in height, has an athletic build and appears well-groomed and polite. Metro Crime Stoppers has offered a reward of up to $1,000 for information leading to the attacker's arrest and indictment.

In addition to Thursday night's attack, on Tuesday, a 61-year-old woman was raped in her kitchen by a man who entered her apartment by asking to use her telephone, police said.

On Sept. 11, a 75-year-old woman was attacked in her home just west of Randallstown. Her assailant managed to slip into the kitchen as she carried in groceries, police said. The woman was thrown to the floor and sexually assaulted.

On Sept. 4, a man armed with a knife tried to force his way into a house just east of Randallstown as a 25-year-old woman returned home from a local grocery store. The man fled when the woman grabbed the telephone to call for help.